Method for trinitrotoluene manufacture



April 30, 1963 E. SAMUELSEN METHOD FOR TRINITROTOLUENE MANUFACTURE Filed Nov. 16, 1954 2 Sheets-Sheet 1 v INVE TOR. BY M JML METHOD FOR TRINITROTOLUENE MANUFACTURE Filed Nov. 16, 1954 2 Sheets-Sheet 2 Fig.6

ATTOR/Vf) United States atent 3,687,971 METHOD FUR TRENITROTOLUENE MANUFATURE Eirik Samuelsen, Guilaug, Norway Filed Nov. 16, 1954, Ser. No. 469,264 Claims priority, appiication Sweden Dec. 7, 1953 10 Claims. (Qt. 260-645) In conventional methods for the nitration of toluene with different mixtures of nitric acid and sulphuric acid, respectively oleum, in three steps to trinitrotoluene it is commonly found that the yield obtained in practice is about 80% of the theoretical. The main part of the loss is considered to be due to the oxidation of the common nitration products of the toluene by the nitric acid. These oxidation losses are especially important by the nitration of dinitrotoluene to trinitrotoluene resulting in a consumption of 1.5 to 2 times the amount of nitric acid theoretically required for this reaction.

In discontinuous methods for nitration of toluene the conditions are such that, after bringing together nitric acid and nitrateable products, a certain amount of unreacted organic material and nitric acid is found in the charge. As the said reaction components are found in relatively small concentrations a certain secondary reaction time is necessary to obtain the preferred grade of nitration. Especially during this secondary nitration nitric acid may, if present, exert an oxidating action upon already nitrated product being present in a high concentration. These oxidation processes always take place at those temperatures and nitric acid concentrations normally used in practice. The secondary nitration time required also causes a prolongation of the cycle of the apparatus or, which is the same, a reduction of the production capacity.

With a given volume of apparatus the production capacity may be raised by performing the nitration in a continuous process with a simultaneous reduction of the oxidation losses. In such processes for the manufacture of trinitrotoluene nitration acid and toluene are brought together in counter-current in a system of nitrators and separators. The number of nitrators, each with a separator attached, are at least 3, in practice rather 5 or more. Through each such unit the products are carried in the same direction. Such continuous nitration processes bring about shorter detention times, which is of advantage in reducing the oxidation losses, but on the other hand they are troublesome to carry out in such a way that a concentration of dinitrotoluene, low enough, is obtained in the trinitrotoluene.

The present invention is based upon the fact that certain mixtures of nitric acid, sulphuric acid and Water in the nitration acid make it possible to perform the nitration of monoand dinitrotoluene to trinitrotoluene with practically no oxidation losses. According to the invention this achievement can be realized by treating the derivatives of toluene with a nitration acid in which the amounts of sulphuric acid, nitric acid and water are matched in such a way that the concentration of sulphuric acid is maintained within 86-95%, the nitric acid Within 14-0.5% and the amount of water within 0-13.5%.

The nitration acid thus should contain at least 86% sulphuric acid, but at the same time the amounts of nitric acid and water should fall within the limits mentioned. The amounts of nitric acid and water taken together should not exceed 14% of the nitration acid and suitably not amount to more than 11% of the same. Said limits are generically valid for the whole nitration process, but to obtain the best possible result somewhat different ratios ought to be used in the first stage of nitration, by nitrating mononitrotoluene to dinitrotoluene, and in the com tinned nitration rto trinitrotoluene. In order to realize a 3,0810% Patented Apr. 30, 1963 favourable reaction velocity during the nitration the concentration of nitric acid must not be too small. Short reaction times as Well as freedom from oxidation losses are thus realized when the concentration of nitric acid in the nitration acid is higher than 5% but still not exceeds the limits given above.

It may be favourable to perform the trinitration with a nitration acid containing minor amounts of sulphur trioxide, e.g. up to 5% free S0 To obtain a satisfactory result it is of great importance that certain volume ratios are maintained between the acid phase and the toluene derivatives phase. In order to obtain favourable reaction velocities in nitrations it is therefore suitable to perform the nitration in such a way that the acid phase occupies at least and preferably at least of the total reaction mixture volume.

The process according to the invention is performed in a system of reactors and separators. Nitric acid and the toluene derivatives are brought together in countercurrent, while the reaction factors are maintained within the limits mentioned above. In a continuous process the relatively large amounts of sulphuric acid required according to the invention is no economic obstacle. It is suitable to divide the trinitration in a number of separate operations.

In order to maintain a correct acid mixture in the last step of a continuous operation, where trinitrotoluene is withdrawn, it is of predominant importance that an acid mixture somewhat deviating from the acid composition to be maintained in this step is introduced here. Thus a mixture of sulphuric acid and nitric acid very nearly free from water is introduced in said step. For the purpose of keeping the acid at a correct composition in other steps that receive nitration acid from the steps immediately preceding, it has been found suitable to adjust the nitra tion acid by introducing an acid mixture rich in nitric acid and sulphuric acid in one or more of these steps. For the adjustment of the nitration acid in one or more of the first dinitration steps in which the water content of the acid may be higher, it is, however, sufficient if water-free nitric acid is introduced.

In order to obtain a small consumption of sulphuric acid it is suitable that the acid mixture entering that reaction vessel, where finished trinitrotoluene is withdrawn, contains at least 60% of the total amount of sulphuric acid required for the dinitration and the trinitration and not more than 30% of the nitric acid required for the trinitration.

Accordingly a part of the present invention is constituted by the accomplishment of performing the dinitrotoluene nitration as a continuous process, divided in more than two steps in which more than 60% but not more than 75% of the sulphuric acid requirements and up to 20% but not more than 30% of the nitric acid requirements for the trinitration is supplied in the last step in which trinitrotoluene is withdrawn in an acid mixture state almost free from water. The rest of the sulphuric acid required for the process is introduced as a mixture of concentrated nitric acid and oleum with at least 20% free S0 in one or more of those steps where the main part of the reaction of dinitrotoluene to trinitrotoluene takes place.

With the foregoing and other objects in view the invention is illustrated in the following example with simultaneous reference to the appended drawings. FIGURE 1 is a schematic drawing, showing in side view the ar rangement of nitration and separation apparatus in steps for carrying out the invention in an embodyment with six nitration and separation aggregates. FIGURE 2 shows the said arrangement seen from above. FIGURE 3 shows a preferred embodiment with respect to the 3 nitration apparatus in connection with a separation apparatus.

In FIGURES 1 and 2, the nitration apparatus are symbolized by 1 and 2 1 and 2 1 and 2 etc. and the separators by 3 3*, 3 etc. Mononitrotoluene flows from tank A to the mixing part 1 of the first nitrator, through bottom outlet 4 into the other part 2 After partial nitration the mononitrotoluene with nitration acid is introduced into the separator 3 through conduit 5 Separated nitrobody passes then through over-flow pipe 6 into the mixing part 1 of the second nitrator, whereupon the gradually stronger nitrated mononitrotoluene passes the rest of the nitrators and separators leaving the system by over-flow pipe 6.

Nitration acid flows from tank B into the mixing part I of the last nitrator. Together with trinitrotoluene it enters the separator 3 through conduit S and is after separation from finished trinitrotoluene further led by over flow pipe 7 f to the mixing part 1 of the fifth nitrator. The acid passes thus through all the nitrators and separators and finally leaves the system by pipe 7 Part of the acid rising in overflow pipes 7 7*, 7 etc. is recirculated to the mixing part =1 1 1 etc. of the nitrators by pipe-lines 8 8 8 etc. respectively. From tanks C and D additional acid may be introduced to correct the acid composition in the first five nitrators.

In FIGURE 3 one nitrator and attached separator is shown in a vertical section. In the mixing part 1 of the nitrator a pumping and mixing wheel 410 is arranged mounted on a shaft- 11 with bearings 12 and driving wheel 13. The mixing part -1 communicates with the part 2 through a bottom pipe 4. Each leg of the nitrator is equipped with temperating means '14 and 15 consisting of double-walled pipes in which water or liquid of desired temperature can be introduced. When the pumping and mixing wheel :10 is in operation the liquid level will rise in the leg 2. This level is held constant by an overflow pipe 9 bringing liquid back to the mixing leg 1. From the leg-2 liquid is withdrawn by pipe 5 into the separator =3 in proportion to liquid introduced in the mixing. part 1. In the mixing part 1 of the nitrator are means 16, 17, 18, 19 to introduce nitrobody, nitration acid, complementary acid etc, In the separator 3 the mixture or dispersion from the nitrator is separated by gravity. The specific lighter nitrobody leaves the separator through overflow pipe 6. The heavier acid accumulates at the bottom and is from there withdrawn with an overflow pipe 7. In order to obtain a volume ratio between nitrobody and acid phase, independent of the primarily introduced nitrobody and acid phase, part of 'the separated acid is returned to the nitrator. The overflow pipe 7 has thus a branch 8 connected with pipe 19 in the mixing part 1. The liquid fiow, according to higher level in separator respectively overflow pipe 7, can be regulated by valve.

By regulating the temperatures and flow velocities of the cooling and heating mediums the following approximate temperatures are maintained in running the process:

In 1 2 and '3 c. 65 C. In 1*, 2 and 3 0. 75 C. In 1, 2 and 3 c. 80 C. In 1 2 and 3 0. 85 C. In 1 2 and 3 c. 90 C. In 1 2 and 3 0. 90 C.

All nitrators are preferably of equal size and in this example with a volume of about 36 liters.

In starting up, the first two reactors 1 2 and 1 2 and separators 3 and 3 are filled with nitration acid containing about 87% sulphuric acid, 5% nitric acid and 8% water and the rest of the reactors and separators with an acid mixture containing about 91.5% sulphuric acid, 8% nitric acid and 0.5% Water. By starting the nitration, mononitrotoluene is first introduced from tank A at a rate .0f*0 .70 kg. per minute. Within 5 minutes pure nitric acid is introduced from tank D, at a rate of 0.09 kg. per minute. When nitration products begin to leave separator 3i making for nitrator 1 2 addition of nitric acid from tank D to the last named nitrator is started at a rate of 0.187 kg. per minute.

A mixture of concentrated nitric acid and oleum, the latter containing 25% free S0 with the composition of 45.4% nitric acid, 13.5% free S0 and 57.6% total sulphuric acid is supplied to the following three nitrators from tank C. When nitration products begin to flow from a separator to the following nitrator, the acid supply to this reactor is started at the following flow-rates:

To nitrator 1, 2: 0.168 kg. nitric acid and 0.213 kg.

total sulphuric acid per minute.

To nitrator 1 2 0.122 kg. nitric acid and 0.155 kg.

total sulphuric acid per minute.

To nitrator 1 2 0.030 kg. nitric acid and 0.038 kg.

total sulphuric acid per minute.

As soon as the trinitrotoluene starts to leave the system by overflow pipe o a nitration acid is introduced from tank B containing 9l.6% sulphuric acid, 8% nitric acid and 0.4% water, so that the following amounts enter the nitrator per minute: 0.905 kg. sulphuric acid, 0.079 kg. nitric acid and 0.004 kg. water.

During the continuous operation the additions of acid are kept at the rates just mentioned. In nitrator 1 2 the result will be an acid phase with a volume of about 92.5% of the total volume of the reaction mixture; in the rest of the reactors the acid phase occupies a somewhat greater part of the volume. Neglecting the small amount of nitrous acid formed, the acids in the difierent reactors then will have the following compositions expressed as percent by weight of the sum of nitric acid,

sulphurlc acid and water.

Sulphuric Nitric Water, In nitrator aci acid, percent percent percent With the process factors given 0.98-1.0 kg. trinitrotoluene is produced in the system per minute. Taking into consideration the c. 0.1 kg. of unreacted mononitrotoluene returning in the process the yield of trinitrotoluene represents up to 97-99% of the theoretical.

The trinitrotoluene leaving the system is washed with water, sodiumbicarbonate solution, sodiumsulphite solution'and again with water, suitably in a continuous process, and is finally dried. If an unfractionated mixture of mononitrotoluene isomers is being used as raw material in the form it is obtained from the nitration of toluene, a trinitrotoluene with a melting point of about 7 8.7 C. results; In the case a product free from metanitrotoluene, e.g. pure ortonitrotoluene, is being used a trinitrotoluene with a melting point of 80.6 C. results.

It is to be understood that the foregoing detailed description is given merely byway of illustration and that the process may be modified in numerous ways without departing from the spirit of the invention. Thus the number of reactors may be varied, for instance 5-6 or more apparatus can be used in the trinitration stage. Less than three reactors totally, however, is not recommended. If reducing the number of reactors the flow-rates of nitrotoluene and acid should also be reduced. Other means to transport nitrobody and nitration acid in countercurrent may be used. For instance gravity fiow of the nitrobody with pumping of the acid phase may be used.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with nitration acid, with separation of nitrobody and acid after each nitration step, the nitration being performed with nitration acids containing 8695% sulphuric acid, 14-05% nitric acid and 043.5% water, calculated on nitrobody free acid mixture.

2. Process of making trinitrotoluene by stepwise nitration of dinitrotoluene in countercurrent with nitration acids, with separation of nitrobody and acid after each nitration step the nitration being performed with nitration acids containing 869'5% sulfuric acid, 14-5% nitric acid and 09% water, calculated on nitrobody free acid.

3. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with nitration acid, with separation of nitrobody and acid after each nitration step, the nitration being performed with nitration acids in which the sum of nitric acid and water content does not exceed 11%, calculated on nitrobody free acid mixture.

4. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with nitration acid, with separation of nitrobody and acid after each nitration step, the nitration of dinitrotoluenes being performed with waterfree nitration acids containing 14-5% nitric acid and 86-95% sulphuric acid with minor amounts of free sulphur trioxide.

5. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with nitration acid, containing 86-95% sulphuric acid, 14-05% nitric acid and 043.5% Water, with separation of nitrobody and acid after each nitration step and partly recirculating the separated acid to the nitration.

6. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with a nitration acid, containing 36-95% sulphuric acid, 145% nitric acid and 09% water, with separation of nitrobody and acid after each nitration step and partly recirculating the separated acid to the nitration step.

7. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with nitration acid, in which the sum of nitric acid and water does not exceed 11%, with separation of nitrobody and acid after each nitration step and partly recirculating the separated acid to the nitration.

8. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with nitration acid, with separation of nitrobody and acid after each nitration step and partly recirculating the separated acid to the nitration, the nitration of dinitrotoluene being performed with a waterfree nitration acid containing 14-5% nitric acid and 8695% sulphuric acid with minor amounts of free sulphur trioxide.

9. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with nitration acid, with separation of nitrobody and acid after each nitration step and recirculating the separated acid to the nitration step in such quantities that the acid phase in the nitration miXure amounts to not less than 80 of the total volume of the mixture.

10. Process of making trinitrotoluene by stepwise nitration of nitrotoluenes in countercurrent with nitration acid, with separation of nitrobody and acid after the nitration steps, the nitration acid introduced in the last step, from which trinitrotoluene is withdrawn, containing -75% of the total amount of sulphuric acid necessary for the whole process and not more than 20-30% of the total amount of nitric acid necessary for the nitration of dinitrotoluene, the desired composition of nitration acid in the other steps being obtained by introducing complementary acids.

References Cited in the file of this patent UNITED STATES PATENTS 483,709 Beck et a1 Oct. 4, 1892 1,297,170 Holley et al Mar. 11, 1919 2,256,999 Castner Sept. 23, 1941 2,402,180 Papazoni June 18, 1946 2,445,741 Franz et al. July 20, 1948 2,475,095 Hoek July 5, 1949 

1. PROCESS OF MAKING TRINITROTOLUENE BY STEPWISE NITRATION OF NITROTOLUENES IN COUNTERCURRENT WITH NITRATION ACIDS WITH SEPARATION OF NITROBOD AND ACID AFTER EACH NITRATION STEP, THE NITRATION BEING PERFORMED WITH NITRATION ACIDS CONTAINING 86-95% SULPHURIC ACIS, 14-.05% NITRIC ACID AND 0-13.5% WATER, CALCULATED ON NITROBODY FREE ACID MIXTURE. 